Osf or pure spy have nothing to lose. You can pin their spies, but it's like assassinates. It doesn't do much because it doesn't lock up any $.
Beat their attack builds. There's no such thing as a spy only clan which doesn't have a main clan that can be exploited. Typically you can go after it one of 2 ways. Either take down their weak members and break their spirit or take down the big players and break their ability to wage an effective war.
If you suspect their large players are ballers I'd hit them on the first round of sneak attacks once you determine their clan. Going for the weaker players is asking for a pounding if you leave strong war pros who are active still standing.
Intelligence on a clan is an asset too.
If you can't beat them join them. Send your spy alt in their clan to figure out who the targets are and put a stop to it
There are plenty of ways for a determined clan to get what they want.
I've farmed all the people who wrote 'protected' on a guy's wall once just because he made me mad and he didn't seem to be active. His buddies didn't like it one bit. Smashing his pals put a stop to the issue real quick.
Oh, one last point. I get 3 requests a month to stop hitting from my friends because I hit actives on the battle list. This is about the worst way to get rid of me. Don't waste my friend's time. Chances are I've already moved on anyhow and now you're telling me you hated it so I'll come back for a week.